The energy conversion methods of x ray detectors can be divided into two types: indirect conversion flat panel detectors (indirect FPD) and direct conversion flat panel detectors (directFPD).
Indirect conversion flat panel detector
The indirect conversion flat panel detector consists of a scintillation crystal coating such as cesium iodide and a thin film transistor (Th n Film T ransistor, T FT) or charge coupled device (C harge Coupling Device, C CD) or complementary metal oxide semiconductor (Com plem en tary M etal Oxide Semi-Conductor (CM OS). The working process of the indirect conversion flat panel detector is generally divided into two steps. First, the scintillation crystal coating converts the X-ray energy into visible light; secondly, the TF T or C CD, or C MO S converts the visible light into an electrical signal. Since visible light will scatter during this process, it will have a certain effect on the spatial resolution. Although the scintillator is processed into columns in the new process to improve the use of X-rays and reduce scattering, the influence of scattered light on spatial resolution cannot be completely eliminated.
Direct conversion x ray detector
The direct conversion x ray detector is mainly composed of an amorphous selenium layer (Am orph ou S Selenium, a-S e) T FT. The incident X-rays cause the selenium layer to generate electron-hole pairs. Under the action of an applied bias field, the electron and hole pairs move in opposite directions to form a current, which forms a stored charge in the thin-film transistor. The amount of stored charge in each transistor corresponds to the dose of incident X-rays, and the amount of charge at each point can be known by the readout circuit, and then the X-ray dose at each point. Since amorphous selenium does not produce visible light and has no influence of scattered rays, a relatively high spatial resolution can be obtained.